HAMILTON, Dec 7 — A new large-scale study has found that the amount of time we sleep, including any daytime naps, appears to be linked with our risk of developing cardiovascular disease and even death.

Carried out by a team of international researchers and led by Chuangshi Wang, a Ph D student at McMaster University, Canada, and Peking Union Medical College, China, the new study looked at a total of 116,632 adults aged between 35 and 70 years in 21 countries across North America, Europe, South America, the Middle East, South Asia, South-east Asia, China and Africa who were followed for an average of nearly eight years.

After taking into account other potentially influencing factors, such as age, sex, education, smoking status, alcohol consumption, and a family history of cardiovascular disease, the researchers found that people who slept for longer than the recommended duration of six to eight hours a day had an increased risk of dying or developing diseases of the heart or blood vessels in the brain.

Those who slept a total of eight to nine hours a day had a 5 per cent increased risk compared to those who slept for six to eight hours total a day, and those who slept between nine and ten hours a day had an increased risk of 17 per cent. Those who slept the longest, for more than 10 hours a day, also had the biggest risk, with 41 per cent increased risk of cardiovascular disease or death.

The team also found a 9 per cent increased risk for people who slept a total of six or fewer hours, but this finding was not statistically significant.

"Our study shows that the optimal duration of estimated sleep is six to eight hours per day for adults. Given that this is an observational study that can only show an association rather than proving a causal relationship, we cannot say that too much sleep per se causes cardiovascular diseases. However, too little sleep could be an underlying contributor to death and cases of cardiovascular disease, and too much sleep may indicate underlying conditions that increase risk,” commented Wang.

The findings, published in the European Heart Journal on Wednesday, also showed that taking regular daytime naps was more common in the Middle East, China, Southeast Asia and South America, with the duration of daytime naps varying from mainly 30 to 60 minutes.

"Although daytime napping was associated with higher risks of death or cardiovascular problems in those with sufficient or longer sleep at night, this was not the case in people who slept under six hours at night. In these individuals, a daytime nap seemed to compensate for the lack of sleep at night and to mitigate the risks,” explained Wang.

A UK study published earlier this year also found that sleeping longer than the recommended amount could be bad for your health, with more than eight hours of sleep a night linked with an increased risk of cardiovascular disease and death, compared to sleeping less than seven hours. — AFP-Relaxnews